1. Field of the Invention
The present invention relates to an apparatus and method for handling substrates in a processing system and more particularly to a vacuum chuck mounted on an end effector.
2. Background of the Related Art
The advantages of using automated substrate handling devices, or robots, in the fabrication of integrated circuits to transfer substrates, including silicon substrates, throughout a cluster tool are well established. Such cluster tools typically comprise a plurality of process chambers and at least one factory interface all connected by a transfer chamber. The cluster tool processes substrates sequentially during automatic processing of substrates. Cassettes positioned in the factory interfaces will hold one, or a plurality of substrates. One or more robots in the transfer chamber sequentially remove substrates from the cassettes and transfer the substrate to one of the process chambers in the cluster tool.
The substrates can then be processed using a variety of processes including physical vapor deposition (PVD), chemical vapor deposition (CVD), electroplating, metal layering, or etching. Some electroplating processes present challenges for robot transfer since substrates are typically processed in a face-down position. Electroplating in integrated circuit design was previously limited to the fabrication of lines on circuit boards. Electroplating is now used to fill vias and contact points in sub-quarter micron, multi-level metallization designs.
Robots typically comprise a hub about which the robot rotates, an end effector (commonly called a xe2x80x9cbladexe2x80x9d), and a plurality of hinged robot links that provide for relative translation of the end effector relative to the robot hub. Traditional end effectors, disposed at a distal end of a robot arm, are positioned underneath a substrate to support the substrate. The end effector may contain some type of chuck (for example vacuum or electrostatic) to hold the substrate to the end effector. During manufacture of IC""s, the xe2x80x9cfacexe2x80x9d portion of the substrate is processed such as with implantation to create devices, and with interconnect structures used to connect the devices. Therefore, the xe2x80x9cfrontxe2x80x9d side of the wafer must be maintained as clean as possible, with minimal contact between this from surface and process equipment. The back surface of the wafer, on which relatively little processing occurs, is thus used for substrate storage and transfer.
Cluster tools dealing with such modem processing techniques as electroplating require both face-up and face-down handling of substrates. In such cases, the robot xe2x80x9cflipsxe2x80x9d substrates between a face-up position and a face-down position between certain successive processing steps. Flipping substrates with end effectors in which a vacuum chuck securely holds the substrate is desirable, but is difficult to perform. Also, ensuring that the substrate is held in a secured, aligned position relative to the end effector is desirable so that the robot can transfer the substrate without collisions with other known objects and equipment. Transferring substrates in a secure and aligned position increases throughput by reducing the need to align the substrate in a process chamber and decreases the possibility of dropping and damaging the expensive substrates.
With certain processing equipment, the robot transports a substrate in a face-down position. A vacuum chuck is typically secured as part of an end effector to allow and accelerate wafer flipping and face-down operations. The vacuum chuck uses vacuum suction applied to a vacuum line with one or more holes formed at one end of the end effector to provide vacuum chucking. After the robot inserts a substrate into an appropriate position in the electroplating process chamber in the face-down position, the substrate separates from the vacuum chuck. The robot then removes the end effector from the process chamber after which the chamber is closed and electroplating occurs. Once the substrate completes electroplating, the robot inserts the end effector into the electroplating process chamber above the substrate. The robot moves into an appropriate position and vacuum chucks the substrate to the end effector. The vacuum chucking process in the inverted orientation is called an inverted hand-off. The substrate is then removed from the chamber. The end effector then flips the wafer into a face-up position for further processing. When the robot transfers substrates in a face-up position, the end effector is located underneath the substrate. Gravity helps ensure flush contact between the end effector and a substrate when the substrate is in the face-up position.
One problem encountered in transferring face-down substrates is that it is difficult to align the vacuum chuck of the end effector accurately with the substrate. This difficulty in alignment makes vacuum chucking more complex. Various factors contribute to inaccurate alignment, including inexact calibration of the robot and process chamber misalignments or expansion. Accurate alignment is important in an inverted handoff to provide a good vacuum seal between the end effector and the substrate for reliable vacuum chucking. Inaccurate alignment during inverted hand-offs may result in failed hand-offs, damaged substrates and chambers, and reduced throughput.
Another problem with transporting substrates is that the substrate may be skewed relative to the end effector when picked up by the end effector. If the substrate is correctly aligned with respect to the end effector, then the position of the entire substrate can be determined and used by the robot. If, however, the substrate is skewed relative to the end effector, then the position of the substrate is uncertain during further substrate transporting and processing. Certainty of the substrate position is important for the controller of the robot to ensure precise robot movements and transfers of the substrate and thereby avoid colliding the wafer with the process equipment or mis-positioning the substrate in the equipment. Such collisions often result in the substrate chipping or breaking, and resultant contamination within or damage of the process chamber. Misalignments of the substrate with the end effector following inverted handoffs also increase the probability that the robot will drop the substrate during transfer or further processing.
Therefore, there is a need for a robot that can reliably secure a substrate to the end effector in a manner that ensures proper alignment during inverted operation or flipping of the substrate.
In one aspect, a vacuum chuck supports a substrate on an end effector, the vacuum chuck comprising a position reference structure and a suction cup. The position reference structure is mounted to the surface and comprises a reference surface. The suction cup is located proximate the reference surface and comprising a suction mount. In another aspect, a method of chucking a substrate to a vacuum chuck is provided. The vacuum chuck comprises a suction cup and a position reference structure. The method comprises attaching the suction cup to the substrate to form a seal therebetween. The suction cup is deformed such that the substrate contacts the position reference structure. The substrate is then leveled on the position reference structure.